/*
    * Copyright 2015 The Netty Project
    *
    * The Netty Project licenses this file to you under the Apache License,
    * version 2.0 (the "License"); you may not use this file except in compliance
    * with the License. You may obtain a copy of the License at:
    *
    *   http://www.apache.org/licenses/LICENSE-2.0
    *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
   * License for the specific language governing permissions and limitations
   * under the License.
   */
  package io.netty.channel.epoll;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.ByteBufAllocator;
  import io.netty.channel.Channel;
  import io.netty.channel.ChannelConfig;
  import io.netty.channel.ChannelFuture;
  import io.netty.channel.ChannelFutureListener;
  import io.netty.channel.ChannelMetadata;
  import io.netty.channel.ChannelOutboundBuffer;
  import io.netty.channel.ChannelPipeline;
  import io.netty.channel.ChannelPromise;
  import io.netty.channel.DefaultFileRegion;
  import io.netty.channel.EventLoop;
  import io.netty.channel.FileRegion;
  import io.netty.channel.RecvByteBufAllocator;
  import io.netty.channel.internal.ChannelUtils;
  import io.netty.channel.socket.DuplexChannel;
  import io.netty.channel.unix.FileDescriptor;
  import io.netty.channel.unix.IovArray;
  import io.netty.channel.unix.SocketWritableByteChannel;
  import io.netty.channel.unix.UnixChannelUtil;
  import io.netty.util.internal.PlatformDependent;
  import io.netty.util.internal.StringUtil;
  import io.netty.util.internal.ThrowableUtil;
  import io.netty.util.internal.UnstableApi;
  import io.netty.util.internal.logging.InternalLogger;
  import io.netty.util.internal.logging.InternalLoggerFactory;
  
  import java.io.IOException;
  import java.net.SocketAddress;
  import java.nio.ByteBuffer;
  import java.nio.channels.ClosedChannelException;
  import java.nio.channels.WritableByteChannel;
  import java.util.Queue;
  import java.util.concurrent.Executor;
  
  import static io.netty.channel.internal.ChannelUtils.MAX_BYTES_PER_GATHERING_WRITE_ATTEMPTED_LOW_THRESHOLD;
  import static io.netty.channel.internal.ChannelUtils.WRITE_STATUS_SNDBUF_FULL;
  import static io.netty.channel.unix.FileDescriptor.pipe;
  import static io.netty.util.internal.ObjectUtil.checkNotNull;
  
  public abstract class AbstractEpollStreamChannel extends AbstractEpollChannel implements DuplexChannel {
      private static final ChannelMetadata METADATA = new ChannelMetadata(false, 16);
      private static final String EXPECTED_TYPES =
              " (expected: " + StringUtil.simpleClassName(ByteBuf.class) + ", " +
                      StringUtil.simpleClassName(DefaultFileRegion.class) + ')';
      private static final InternalLogger logger = InternalLoggerFactory.getInstance(AbstractEpollStreamChannel.class);
      private static final ClosedChannelException CLEAR_SPLICE_QUEUE_CLOSED_CHANNEL_EXCEPTION =
              ThrowableUtil.unknownStackTrace(new ClosedChannelException(),
                      AbstractEpollStreamChannel.class, "clearSpliceQueue()");
      private static final ClosedChannelException SPLICE_TO_CLOSED_CHANNEL_EXCEPTION = ThrowableUtil.unknownStackTrace(
              new ClosedChannelException(),
              AbstractEpollStreamChannel.class, "spliceTo(...)");
      private static final ClosedChannelException FAIL_SPLICE_IF_CLOSED_CLOSED_CHANNEL_EXCEPTION =
              ThrowableUtil.unknownStackTrace(new ClosedChannelException(),
              AbstractEpollStreamChannel.class, "failSpliceIfClosed(...)");
      private final Runnable flushTask = new Runnable() {
          @Override
          public void run() {
              // Calling flush0 directly to ensure we not try to flush messages that were added via write(...) in the
              // meantime.
              ((AbstractEpollUnsafe) unsafe()).flush0();
          }
      };
      private Queue<SpliceInTask> spliceQueue;
  
      // Lazy init these if we need to splice(...)
      private FileDescriptor pipeIn;
      private FileDescriptor pipeOut;
  
      private WritableByteChannel byteChannel;
  
      protected AbstractEpollStreamChannel(Channel parent, int fd) {
          this(parent, new LinuxSocket(fd));
      }
  
      protected AbstractEpollStreamChannel(int fd) {
          this(new LinuxSocket(fd));
      }
  
      AbstractEpollStreamChannel(LinuxSocket fd) {
          this(fd, isSoErrorZero(fd));
      }
 
     AbstractEpollStreamChannel(Channel parent, LinuxSocket fd) {
         super(parent, fd, true);
         // Add EPOLLRDHUP so we are notified once the remote peer close the connection.
         flags |= Native.EPOLLRDHUP;
     }
 
     AbstractEpollStreamChannel(Channel parent, LinuxSocket fd, SocketAddress remote) {
         super(parent, fd, remote);
         // Add EPOLLRDHUP so we are notified once the remote peer close the connection.
         flags |= Native.EPOLLRDHUP;
     }
 
     protected AbstractEpollStreamChannel(LinuxSocket fd, boolean active) {
         super(null, fd, active);
         // Add EPOLLRDHUP so we are notified once the remote peer close the connection.
         flags |= Native.EPOLLRDHUP;
     }
 
     @Override
     protected AbstractEpollUnsafe newUnsafe() {
         return new EpollStreamUnsafe();
     }
 
     @Override
     public ChannelMetadata metadata() {
         return METADATA;
     }
 
     /**
      * Splice from this {@link AbstractEpollStreamChannel} to another {@link AbstractEpollStreamChannel}.
      * The {@code len} is the number of bytes to splice. If using {@link Integer#MAX_VALUE} it will
      * splice until the {@link ChannelFuture} was canceled or it was failed.
      *
      * Please note:
      * <ul>
      *   <li>both channels need to be registered to the same {@link EventLoop}, otherwise an
      *   {@link IllegalArgumentException} is thrown. </li>
      *   <li>{@link EpollChannelConfig#getEpollMode()} must be {@link EpollMode#LEVEL_TRIGGERED} for this and the
      *   target {@link AbstractEpollStreamChannel}</li>
      * </ul>
      *
      */
     public final ChannelFuture spliceTo(final AbstractEpollStreamChannel ch, final int len) {
         return spliceTo(ch, len, newPromise());
     }
 
     /**
      * Splice from this {@link AbstractEpollStreamChannel} to another {@link AbstractEpollStreamChannel}.
      * The {@code len} is the number of bytes to splice. If using {@link Integer#MAX_VALUE} it will
      * splice until the {@link ChannelFuture} was canceled or it was failed.
      *
      * Please note:
      * <ul>
      *   <li>both channels need to be registered to the same {@link EventLoop}, otherwise an
      *   {@link IllegalArgumentException} is thrown. </li>
      *   <li>{@link EpollChannelConfig#getEpollMode()} must be {@link EpollMode#LEVEL_TRIGGERED} for this and the
      *   target {@link AbstractEpollStreamChannel}</li>
      * </ul>
      *
      */
     public final ChannelFuture spliceTo(final AbstractEpollStreamChannel ch, final int len,
                                         final ChannelPromise promise) {
         if (ch.eventLoop() != eventLoop()) {
             throw new IllegalArgumentException("EventLoops are not the same.");
         }
         if (len < 0) {
             throw new IllegalArgumentException("len: " + len + " (expected: >= 0)");
         }
         if (ch.config().getEpollMode() != EpollMode.LEVEL_TRIGGERED
                 || config().getEpollMode() != EpollMode.LEVEL_TRIGGERED) {
             throw new IllegalStateException("spliceTo() supported only when using " + EpollMode.LEVEL_TRIGGERED);
         }
         checkNotNull(promise, "promise");
         if (!isOpen()) {
             promise.tryFailure(SPLICE_TO_CLOSED_CHANNEL_EXCEPTION);
         } else {
             addToSpliceQueue(new SpliceInChannelTask(ch, len, promise));
             failSpliceIfClosed(promise);
         }
         return promise;
     }
 
     /**
      * Splice from this {@link AbstractEpollStreamChannel} to another {@link FileDescriptor}.
      * The {@code offset} is the offset for the {@link FileDescriptor} and {@code len} is the
      * number of bytes to splice. If using {@link Integer#MAX_VALUE} it will splice until the
      * {@link ChannelFuture} was canceled or it was failed.
      *
      * Please note:
      * <ul>
      *   <li>{@link EpollChannelConfig#getEpollMode()} must be {@link EpollMode#LEVEL_TRIGGERED} for this
      *   {@link AbstractEpollStreamChannel}</li>
      *   <li>the {@link FileDescriptor} will not be closed after the {@link ChannelFuture} is notified</li>
      *   <li>this channel must be registered to an event loop or {@link IllegalStateException} will be thrown.</li>
      * </ul>
      */
     public final ChannelFuture spliceTo(final FileDescriptor ch, final int offset, final int len) {
         return spliceTo(ch, offset, len, newPromise());
     }
 
     /**
      * Splice from this {@link AbstractEpollStreamChannel} to another {@link FileDescriptor}.
      * The {@code offset} is the offset for the {@link FileDescriptor} and {@code len} is the
      * number of bytes to splice. If using {@link Integer#MAX_VALUE} it will splice until the
      * {@link ChannelFuture} was canceled or it was failed.
      *
      * Please note:
      * <ul>
      *   <li>{@link EpollChannelConfig#getEpollMode()} must be {@link EpollMode#LEVEL_TRIGGERED} for this
      *   {@link AbstractEpollStreamChannel}</li>
      *   <li>the {@link FileDescriptor} will not be closed after the {@link ChannelPromise} is notified</li>
      *   <li>this channel must be registered to an event loop or {@link IllegalStateException} will be thrown.</li>
      * </ul>
      */
     public final ChannelFuture spliceTo(final FileDescriptor ch, final int offset, final int len,
                                         final ChannelPromise promise) {
         if (len < 0) {
             throw new IllegalArgumentException("len: " + len + " (expected: >= 0)");
         }
         if (offset < 0) {
             throw new IllegalArgumentException("offset must be >= 0 but was " + offset);
         }
         if (config().getEpollMode() != EpollMode.LEVEL_TRIGGERED) {
             throw new IllegalStateException("spliceTo() supported only when using " + EpollMode.LEVEL_TRIGGERED);
         }
         checkNotNull(promise, "promise");
         if (!isOpen()) {
             promise.tryFailure(SPLICE_TO_CLOSED_CHANNEL_EXCEPTION);
         } else {
             addToSpliceQueue(new SpliceFdTask(ch, offset, len, promise));
             failSpliceIfClosed(promise);
         }
         return promise;
     }
 
     private void failSpliceIfClosed(ChannelPromise promise) {
         if (!isOpen()) {
             // Seems like the Channel was closed in the meantime try to fail the promise to prevent any
             // cases where a future may not be notified otherwise.
             if (promise.tryFailure(FAIL_SPLICE_IF_CLOSED_CLOSED_CHANNEL_EXCEPTION)) {
                 eventLoop().execute(new Runnable() {
                     @Override
                     public void run() {
                         // Call this via the EventLoop as it is a MPSC queue.
                         clearSpliceQueue();
                     }
                 });
             }
         }
     }
 
     /**
      * Write bytes form the given {@link ByteBuf} to the underlying {@link java.nio.channels.Channel}.
      * @param in the collection which contains objects to write.
      * @param buf the {@link ByteBuf} from which the bytes should be written
      * @return The value that should be decremented from the write quantum which starts at
      * {@link ChannelConfig#getWriteSpinCount()}. The typical use cases are as follows:
      * <ul>
      *     <li>0 - if no write was attempted. This is appropriate if an empty {@link ByteBuf} (or other empty content)
      *     is encountered</li>
      *     <li>1 - if a single call to write data was made to the OS</li>
      *     <li>{@link ChannelUtils#WRITE_STATUS_SNDBUF_FULL} - if an attempt to write data was made to the OS, but
      *     no data was accepted</li>
      * </ul>
      */
     private int writeBytes(ChannelOutboundBuffer in, ByteBuf buf) throws Exception {
         int readableBytes = buf.readableBytes();
         if (readableBytes == 0) {
             in.remove();
             return 0;
         }
 
         if (buf.hasMemoryAddress() || buf.nioBufferCount() == 1) {
             return doWriteBytes(in, buf);
         } else {
             ByteBuffer[] nioBuffers = buf.nioBuffers();
             return writeBytesMultiple(in, nioBuffers, nioBuffers.length, readableBytes,
                     config().getMaxBytesPerGatheringWrite());
         }
     }
 
     private void adjustMaxBytesPerGatheringWrite(long attempted, long written, long oldMaxBytesPerGatheringWrite) {
         // By default we track the SO_SNDBUF when ever it is explicitly set. However some OSes may dynamically change
         // SO_SNDBUF (and other characteristics that determine how much data can be written at once) so we should try
         // make a best effort to adjust as OS behavior changes.
         if (attempted == written) {
             if (attempted << 1 > oldMaxBytesPerGatheringWrite) {
                 config().setMaxBytesPerGatheringWrite(attempted << 1);
             }
         } else if (attempted > MAX_BYTES_PER_GATHERING_WRITE_ATTEMPTED_LOW_THRESHOLD && written < attempted >>> 1) {
             config().setMaxBytesPerGatheringWrite(attempted >>> 1);
         }
     }
 
     /**
      * Write multiple bytes via {@link IovArray}.
      * @param in the collection which contains objects to write.
      * @param array The array which contains the content to write.
      * @return The value that should be decremented from the write quantum which starts at
      * {@link ChannelConfig#getWriteSpinCount()}. The typical use cases are as follows:
      * <ul>
      *     <li>0 - if no write was attempted. This is appropriate if an empty {@link ByteBuf} (or other empty content)
      *     is encountered</li>
      *     <li>1 - if a single call to write data was made to the OS</li>
      *     <li>{@link ChannelUtils#WRITE_STATUS_SNDBUF_FULL} - if an attempt to write data was made to the OS, but
      *     no data was accepted</li>
      * </ul>
      * @throws IOException If an I/O exception occurs during write.
      */
     private int writeBytesMultiple(ChannelOutboundBuffer in, IovArray array) throws IOException {
         final long expectedWrittenBytes = array.size();
         assert expectedWrittenBytes != 0;
         final int cnt = array.count();
         assert cnt != 0;
 
         final long localWrittenBytes = socket.writevAddresses(array.memoryAddress(0), cnt);
         if (localWrittenBytes > 0) {
             adjustMaxBytesPerGatheringWrite(expectedWrittenBytes, localWrittenBytes, array.maxBytes());
             in.removeBytes(localWrittenBytes);
             return 1;
         }
         return WRITE_STATUS_SNDBUF_FULL;
     }
 
     /**
      * Write multiple bytes via {@link ByteBuffer} array.
      * @param in the collection which contains objects to write.
      * @param nioBuffers The buffers to write.
      * @param nioBufferCnt The number of buffers to write.
      * @param expectedWrittenBytes The number of bytes we expect to write.
      * @param maxBytesPerGatheringWrite The maximum number of bytes we should attempt to write.
      * @return The value that should be decremented from the write quantum which starts at
      * {@link ChannelConfig#getWriteSpinCount()}. The typical use cases are as follows:
      * <ul>
      *     <li>0 - if no write was attempted. This is appropriate if an empty {@link ByteBuf} (or other empty content)
      *     is encountered</li>
      *     <li>1 - if a single call to write data was made to the OS</li>
      *     <li>{@link ChannelUtils#WRITE_STATUS_SNDBUF_FULL} - if an attempt to write data was made to the OS, but
      *     no data was accepted</li>
      * </ul>
      * @throws IOException If an I/O exception occurs during write.
      */
     private int writeBytesMultiple(
             ChannelOutboundBuffer in, ByteBuffer[] nioBuffers, int nioBufferCnt, long expectedWrittenBytes,
             long maxBytesPerGatheringWrite) throws IOException {
         assert expectedWrittenBytes != 0;
         if (expectedWrittenBytes > maxBytesPerGatheringWrite) {
             expectedWrittenBytes = maxBytesPerGatheringWrite;
         }
 
         final long localWrittenBytes = socket.writev(nioBuffers, 0, nioBufferCnt, expectedWrittenBytes);
         if (localWrittenBytes > 0) {
             adjustMaxBytesPerGatheringWrite(expectedWrittenBytes, localWrittenBytes, maxBytesPerGatheringWrite);
             in.removeBytes(localWrittenBytes);
             return 1;
         }
         return WRITE_STATUS_SNDBUF_FULL;
     }
 
     /**
      * Write a {@link DefaultFileRegion}
      * @param in the collection which contains objects to write.
      * @param region the {@link DefaultFileRegion} from which the bytes should be written
      * @return The value that should be decremented from the write quantum which starts at
      * {@link ChannelConfig#getWriteSpinCount()}. The typical use cases are as follows:
      * <ul>
      *     <li>0 - if no write was attempted. This is appropriate if an empty {@link ByteBuf} (or other empty content)
      *     is encountered</li>
      *     <li>1 - if a single call to write data was made to the OS</li>
      *     <li>{@link ChannelUtils#WRITE_STATUS_SNDBUF_FULL} - if an attempt to write data was made to the OS, but
      *     no data was accepted</li>
      * </ul>
      */
     private int writeDefaultFileRegion(ChannelOutboundBuffer in, DefaultFileRegion region) throws Exception {
         final long regionCount = region.count();
         if (region.transferred() >= regionCount) {
             in.remove();
             return 0;
         }
 
         final long offset = region.transferred();
         final long flushedAmount = socket.sendFile(region, region.position(), offset, regionCount - offset);
         if (flushedAmount > 0) {
             in.progress(flushedAmount);
             if (region.transferred() >= regionCount) {
                 in.remove();
             }
             return 1;
         }
         return WRITE_STATUS_SNDBUF_FULL;
     }
 
     /**
      * Write a {@link FileRegion}
      * @param in the collection which contains objects to write.
      * @param region the {@link FileRegion} from which the bytes should be written
      * @return The value that should be decremented from the write quantum which starts at
      * {@link ChannelConfig#getWriteSpinCount()}. The typical use cases are as follows:
      * <ul>
      *     <li>0 - if no write was attempted. This is appropriate if an empty {@link ByteBuf} (or other empty content)
      *     is encountered</li>
      *     <li>1 - if a single call to write data was made to the OS</li>
      *     <li>{@link ChannelUtils#WRITE_STATUS_SNDBUF_FULL} - if an attempt to write data was made to the OS, but
      *     no data was accepted</li>
      * </ul>
      */
     private int writeFileRegion(ChannelOutboundBuffer in, FileRegion region) throws Exception {
         if (region.transferred() >= region.count()) {
             in.remove();
             return 0;
         }
 
         if (byteChannel == null) {
             byteChannel = new EpollSocketWritableByteChannel();
         }
         final long flushedAmount = region.transferTo(byteChannel, region.transferred());
         if (flushedAmount > 0) {
             in.progress(flushedAmount);
             if (region.transferred() >= region.count()) {
                 in.remove();
             }
             return 1;
         }
         return WRITE_STATUS_SNDBUF_FULL;
     }
 
     @Override
     protected void doWrite(ChannelOutboundBuffer in) throws Exception {
         int writeSpinCount = config().getWriteSpinCount();
         do {
             final int msgCount = in.size();
             // Do gathering write if the outbound buffer entries start with more than one ByteBuf.
             if (msgCount > 1 && in.current() instanceof ByteBuf) {
                 writeSpinCount -= doWriteMultiple(in);
             } else if (msgCount == 0) {
                 // Wrote all messages.
                 clearFlag(Native.EPOLLOUT);
                 // Return here so we not set the EPOLLOUT flag.
                 return;
             } else {  // msgCount == 1
                 writeSpinCount -= doWriteSingle(in);
             }
 
             // We do not break the loop here even if the outbound buffer was flushed completely,
             // because a user might have triggered another write and flush when we notify his or her
             // listeners.
         } while (writeSpinCount > 0);
 
         if (writeSpinCount == 0) {
             // It is possible that we have set EPOLLOUT, woken up by EPOLL because the socket is writable, and then use
             // our write quantum. In this case we no longer want to set the EPOLLOUT flag because the socket is still
             // writable (as far as we know). We will find out next time we attempt to write if the socket is writable
             // and set the EPOLLOUT if necessary.
             clearFlag(Native.EPOLLOUT);
 
             // We used our writeSpin quantum, and should try to write again later.
             eventLoop().execute(flushTask);
         } else {
             // Underlying descriptor can not accept all data currently, so set the EPOLLOUT flag to be woken up
             // when it can accept more data.
             setFlag(Native.EPOLLOUT);
         }
     }
 
     /**
      * Attempt to write a single object.
      * @param in the collection which contains objects to write.
      * @return The value that should be decremented from the write quantum which starts at
      * {@link ChannelConfig#getWriteSpinCount()}. The typical use cases are as follows:
      * <ul>
      *     <li>0 - if no write was attempted. This is appropriate if an empty {@link ByteBuf} (or other empty content)
      *     is encountered</li>
      *     <li>1 - if a single call to write data was made to the OS</li>
      *     <li>{@link ChannelUtils#WRITE_STATUS_SNDBUF_FULL} - if an attempt to write data was made to the OS, but
      *     no data was accepted</li>
      * </ul>
      * @throws Exception If an I/O error occurs.
      */
     protected int doWriteSingle(ChannelOutboundBuffer in) throws Exception {
         // The outbound buffer contains only one message or it contains a file region.
         Object msg = in.current();
         if (msg instanceof ByteBuf) {
             return writeBytes(in, (ByteBuf) msg);
         } else if (msg instanceof DefaultFileRegion) {
             return writeDefaultFileRegion(in, (DefaultFileRegion) msg);
         } else if (msg instanceof FileRegion) {
             return writeFileRegion(in, (FileRegion) msg);
         } else if (msg instanceof SpliceOutTask) {
             if (!((SpliceOutTask) msg).spliceOut()) {
                 return WRITE_STATUS_SNDBUF_FULL;
             }
             in.remove();
             return 1;
         } else {
             // Should never reach here.
             throw new Error();
         }
     }
 
     /**
      * Attempt to write multiple {@link ByteBuf} objects.
      * @param in the collection which contains objects to write.
      * @return The value that should be decremented from the write quantum which starts at
      * {@link ChannelConfig#getWriteSpinCount()}. The typical use cases are as follows:
      * <ul>
      *     <li>0 - if no write was attempted. This is appropriate if an empty {@link ByteBuf} (or other empty content)
      *     is encountered</li>
      *     <li>1 - if a single call to write data was made to the OS</li>
      *     <li>{@link ChannelUtils#WRITE_STATUS_SNDBUF_FULL} - if an attempt to write data was made to the OS, but
      *     no data was accepted</li>
      * </ul>
      * @throws Exception If an I/O error occurs.
      */
     private int doWriteMultiple(ChannelOutboundBuffer in) throws Exception {
         final long maxBytesPerGatheringWrite = config().getMaxBytesPerGatheringWrite();
         IovArray array = ((EpollEventLoop) eventLoop()).cleanIovArray();
         array.maxBytes(maxBytesPerGatheringWrite);
         in.forEachFlushedMessage(array);
 
         if (array.count() >= 1) {
             // TODO: Handle the case where cnt == 1 specially.
             return writeBytesMultiple(in, array);
         }
         // cnt == 0, which means the outbound buffer contained empty buffers only.
         in.removeBytes(0);
         return 0;
     }
 
     @Override
     protected Object filterOutboundMessage(Object msg) {
         if (msg instanceof ByteBuf) {
             ByteBuf buf = (ByteBuf) msg;
             return UnixChannelUtil.isBufferCopyNeededForWrite(buf)? newDirectBuffer(buf): buf;
         }
 
         if (msg instanceof FileRegion || msg instanceof SpliceOutTask) {
             return msg;
         }
 
         throw new UnsupportedOperationException(
                 "unsupported message type: " + StringUtil.simpleClassName(msg) + EXPECTED_TYPES);
     }
 
     @UnstableApi
     @Override
     protected final void doShutdownOutput() throws Exception {
         socket.shutdown(false, true);
     }
 
     private void shutdownInput0(final ChannelPromise promise) {
         try {
             socket.shutdown(true, false);
             promise.setSuccess();
         } catch (Throwable cause) {
             promise.setFailure(cause);
         }
     }
 
     @Override
     public boolean isOutputShutdown() {
         return socket.isOutputShutdown();
     }
 
     @Override
     public boolean isInputShutdown() {
         return socket.isInputShutdown();
     }
 
     @Override
     public boolean isShutdown() {
         return socket.isShutdown();
     }
 
     @Override
     public ChannelFuture shutdownOutput() {
         return shutdownOutput(newPromise());
     }
 
     @Override
     public ChannelFuture shutdownOutput(final ChannelPromise promise) {
         EventLoop loop = eventLoop();
         if (loop.inEventLoop()) {
             ((AbstractUnsafe) unsafe()).shutdownOutput(promise);
         } else {
             loop.execute(new Runnable() {
                 @Override
                 public void run() {
                     ((AbstractUnsafe) unsafe()).shutdownOutput(promise);
                 }
             });
         }
 
         return promise;
     }
 
     @Override
     public ChannelFuture shutdownInput() {
         return shutdownInput(newPromise());
     }
 
     @Override
     public ChannelFuture shutdownInput(final ChannelPromise promise) {
         Executor closeExecutor = ((EpollStreamUnsafe) unsafe()).prepareToClose();
         if (closeExecutor != null) {
             closeExecutor.execute(new Runnable() {
                 @Override
                 public void run() {
                     shutdownInput0(promise);
                 }
             });
         } else {
             EventLoop loop = eventLoop();
             if (loop.inEventLoop()) {
                 shutdownInput0(promise);
             } else {
                 loop.execute(new Runnable() {
                     @Override
                     public void run() {
                         shutdownInput0(promise);
                     }
                 });
             }
         }
         return promise;
     }
 
     @Override
     public ChannelFuture shutdown() {
         return shutdown(newPromise());
     }
 
     @Override
     public ChannelFuture shutdown(final ChannelPromise promise) {
         ChannelFuture shutdownOutputFuture = shutdownOutput();
         if (shutdownOutputFuture.isDone()) {
             shutdownOutputDone(shutdownOutputFuture, promise);
         } else {
             shutdownOutputFuture.addListener(new ChannelFutureListener() {
                 @Override
                 public void operationComplete(final ChannelFuture shutdownOutputFuture) throws Exception {
                     shutdownOutputDone(shutdownOutputFuture, promise);
                 }
             });
         }
         return promise;
     }
 
     private void shutdownOutputDone(final ChannelFuture shutdownOutputFuture, final ChannelPromise promise) {
         ChannelFuture shutdownInputFuture = shutdownInput();
         if (shutdownInputFuture.isDone()) {
             shutdownDone(shutdownOutputFuture, shutdownInputFuture, promise);
         } else {
             shutdownInputFuture.addListener(new ChannelFutureListener() {
                 @Override
                 public void operationComplete(ChannelFuture shutdownInputFuture) throws Exception {
                     shutdownDone(shutdownOutputFuture, shutdownInputFuture, promise);
                 }
             });
         }
     }
 
     private static void shutdownDone(ChannelFuture shutdownOutputFuture,
                               ChannelFuture shutdownInputFuture,
                               ChannelPromise promise) {
         Throwable shutdownOutputCause = shutdownOutputFuture.cause();
         Throwable shutdownInputCause = shutdownInputFuture.cause();
         if (shutdownOutputCause != null) {
             if (shutdownInputCause != null) {
                 logger.debug("Exception suppressed because a previous exception occurred.",
                         shutdownInputCause);
             }
             promise.setFailure(shutdownOutputCause);
         } else if (shutdownInputCause != null) {
             promise.setFailure(shutdownInputCause);
         } else {
             promise.setSuccess();
         }
     }
 
     @Override
     protected void doClose() throws Exception {
         try {
             // Calling super.doClose() first so spliceTo(...) will fail on next call.
             super.doClose();
         } finally {
             safeClosePipe(pipeIn);
             safeClosePipe(pipeOut);
             clearSpliceQueue();
         }
     }
 
     private void clearSpliceQueue() {
         if (spliceQueue == null) {
             return;
         }
         for (;;) {
             SpliceInTask task = spliceQueue.poll();
             if (task == null) {
                 break;
             }
             task.promise.tryFailure(CLEAR_SPLICE_QUEUE_CLOSED_CHANNEL_EXCEPTION);
         }
     }
 
     private static void safeClosePipe(FileDescriptor fd) {
         if (fd != null) {
             try {
                 fd.close();
             } catch (IOException e) {
                 if (logger.isWarnEnabled()) {
                     logger.warn("Error while closing a pipe", e);
                 }
             }
         }
     }
 
     class EpollStreamUnsafe extends AbstractEpollUnsafe {
         // Overridden here just to be able to access this method from AbstractEpollStreamChannel
         @Override
         protected Executor prepareToClose() {
             return super.prepareToClose();
         }
 
         private void handleReadException(ChannelPipeline pipeline, ByteBuf byteBuf, Throwable cause, boolean close,
                 EpollRecvByteAllocatorHandle allocHandle) {
             if (byteBuf != null) {
                 if (byteBuf.isReadable()) {
                     readPending = false;
                     pipeline.fireChannelRead(byteBuf);
                 } else {
                     byteBuf.release();
                 }
             }
             allocHandle.readComplete();
             pipeline.fireChannelReadComplete();
             pipeline.fireExceptionCaught(cause);
             if (close || cause instanceof IOException) {
                 shutdownInput(false);
             }
         }
 
         @Override
         EpollRecvByteAllocatorHandle newEpollHandle(RecvByteBufAllocator.ExtendedHandle handle) {
             return new EpollRecvByteAllocatorStreamingHandle(handle);
         }
 
         @Override
         void epollInReady() {
             final ChannelConfig config = config();
             if (shouldBreakEpollInReady(config)) {
                 clearEpollIn0();
                 return;
             }
             final EpollRecvByteAllocatorHandle allocHandle = recvBufAllocHandle();
             allocHandle.edgeTriggered(isFlagSet(Native.EPOLLET));
 
             final ChannelPipeline pipeline = pipeline();
             final ByteBufAllocator allocator = config.getAllocator();
             allocHandle.reset(config);
             epollInBefore();
 
             ByteBuf byteBuf = null;
             boolean close = false;
             try {
                 do {
                     if (spliceQueue != null) {
                         SpliceInTask spliceTask = spliceQueue.peek();
                         if (spliceTask != null) {
                             if (spliceTask.spliceIn(allocHandle)) {
                                 // We need to check if it is still active as if not we removed all SpliceTasks in
                                 // doClose(...)
                                 if (isActive()) {
                                     spliceQueue.remove();
                                 }
                                 continue;
                             } else {
                                 break;
                             }
                         }
                     }
 
                     // we use a direct buffer here as the native implementations only be able
                     // to handle direct buffers.
                     byteBuf = allocHandle.allocate(allocator);
                     allocHandle.lastBytesRead(doReadBytes(byteBuf));
                     if (allocHandle.lastBytesRead() <= 0) {
                         // nothing was read, release the buffer.
                         byteBuf.release();
                         byteBuf = null;
                         close = allocHandle.lastBytesRead() < 0;
                         if (close) {
                             // There is nothing left to read as we received an EOF.
                             readPending = false;
                         }
                         break;
                     }
                     allocHandle.incMessagesRead(1);
                     readPending = false;
                     pipeline.fireChannelRead(byteBuf);
                     byteBuf = null;
 
                     if (shouldBreakEpollInReady(config)) {
                         // We need to do this for two reasons:
                         //
                         // - If the input was shutdown in between (which may be the case when the user did it in the
                         //   fireChannelRead(...) method we should not try to read again to not produce any
                         //   miss-leading exceptions.
                         //
                         // - If the user closes the channel we need to ensure we not try to read from it again as
                         //   the filedescriptor may be re-used already by the OS if the system is handling a lot of
                         //   concurrent connections and so needs a lot of filedescriptors. If not do this we risk
                         //   reading data from a filedescriptor that belongs to another socket then the socket that
                         //   was "wrapped" by this Channel implementation.
                         break;
                     }
                 } while (allocHandle.continueReading());
 
                 allocHandle.readComplete();
                 pipeline.fireChannelReadComplete();
 
                 if (close) {
                     shutdownInput(false);
                 }
             } catch (Throwable t) {
                 handleReadException(pipeline, byteBuf, t, close, allocHandle);
             } finally {
                 epollInFinally(config);
             }
         }
     }
 
     private void addToSpliceQueue(final SpliceInTask task) {
         EventLoop eventLoop = eventLoop();
         if (eventLoop.inEventLoop()) {
             addToSpliceQueue0(task);
         } else {
             eventLoop.execute(new Runnable() {
                 @Override
                 public void run() {
                     addToSpliceQueue0(task);
                 }
             });
         }
     }
 
     private void addToSpliceQueue0(SpliceInTask task) {
         if (spliceQueue == null) {
             spliceQueue = PlatformDependent.newMpscQueue();
         }
         spliceQueue.add(task);
     }
 
     protected abstract class SpliceInTask {
         final ChannelPromise promise;
         int len;
 
         protected SpliceInTask(int len, ChannelPromise promise) {
             this.promise = promise;
             this.len = len;
         }
 
         abstract boolean spliceIn(RecvByteBufAllocator.Handle handle);
 
         protected final int spliceIn(FileDescriptor pipeOut, RecvByteBufAllocator.Handle handle) throws IOException {
             // calculate the maximum amount of data we are allowed to splice
             int length = Math.min(handle.guess(), len);
             int splicedIn = 0;
             for (;;) {
                 // Splicing until there is nothing left to splice.
                 int localSplicedIn = Native.splice(socket.intValue(), -1, pipeOut.intValue(), -1, length);
                 if (localSplicedIn == 0) {
                     break;
                 }
                 splicedIn += localSplicedIn;
                 length -= localSplicedIn;
             }
 
             return splicedIn;
         }
     }
 
     // Let it directly implement channelFutureListener as well to reduce object creation.
     private final class SpliceInChannelTask extends SpliceInTask implements ChannelFutureListener {
         private final AbstractEpollStreamChannel ch;
 
         SpliceInChannelTask(AbstractEpollStreamChannel ch, int len, ChannelPromise promise) {
             super(len, promise);
             this.ch = ch;
         }
 
         @Override
         public void operationComplete(ChannelFuture future) throws Exception {
             if (!future.isSuccess()) {
                 promise.setFailure(future.cause());
             }
         }
 
         @Override
         public boolean spliceIn(RecvByteBufAllocator.Handle handle) {
             assert ch.eventLoop().inEventLoop();
             if (len == 0) {
                 promise.setSuccess();
                 return true;
             }
             try {
                 // We create the pipe on the target channel as this will allow us to just handle pending writes
                 // later in a correct fashion without get into any ordering issues when spliceTo(...) is called
                 // on multiple Channels pointing to one target Channel.
                 FileDescriptor pipeOut = ch.pipeOut;
                 if (pipeOut == null) {
                     // Create a new pipe as non was created before.
                     FileDescriptor[] pipe = pipe();
                     ch.pipeIn = pipe[0];
                     pipeOut = ch.pipeOut = pipe[1];
                 }
 
                 int splicedIn = spliceIn(pipeOut, handle);
                 if (splicedIn > 0) {
                     // Integer.MAX_VALUE is a special value which will result in splice forever.
                     if (len != Integer.MAX_VALUE) {
                         len -= splicedIn;
                     }
 
                     // Depending on if we are done with splicing inbound data we set the right promise for the
                     // outbound splicing.
                     final ChannelPromise splicePromise;
                     if (len == 0) {
                         splicePromise = promise;
                     } else {
                         splicePromise = ch.newPromise().addListener(this);
                     }
 
                     boolean autoRead = config().isAutoRead();
 
                     // Just call unsafe().write(...) and flush() as we not want to traverse the whole pipeline for this
                     // case.
                     ch.unsafe().write(new SpliceOutTask(ch, splicedIn, autoRead), splicePromise);
                     ch.unsafe().flush();
                     if (autoRead && !splicePromise.isDone()) {
                         // Write was not done which means the target channel was not writable. In this case we need to
                         // disable reading until we are done with splicing to the target channel because:
                         //
                         // - The user may want to to trigger another splice operation once the splicing was complete.
                         config().setAutoRead(false);
                     }
                 }
 
                 return len == 0;
             } catch (Throwable cause) {
                 promise.setFailure(cause);
                 return true;
             }
         }
     }
 
     private final class SpliceOutTask {
         private final AbstractEpollStreamChannel ch;
         private final boolean autoRead;
         private int len;
 
         SpliceOutTask(AbstractEpollStreamChannel ch, int len, boolean autoRead) {
             this.ch = ch;
             this.len = len;
             this.autoRead = autoRead;
         }
 
         public boolean spliceOut() throws Exception {
             assert ch.eventLoop().inEventLoop();
             try {
                 int splicedOut = Native.splice(ch.pipeIn.intValue(), -1, ch.socket.intValue(), -1, len);
                 len -= splicedOut;
                 if (len == 0) {
                     if (autoRead) {
                         // AutoRead was used and we spliced everything so start reading again
                         config().setAutoRead(true);
                     }
                     return true;
                 }
                 return false;
             } catch (IOException e) {
                 if (autoRead) {
                     // AutoRead was used and we spliced everything so start reading again
                     config().setAutoRead(true);
                 }
                 throw e;
             }
         }
     }
 
     private final class SpliceFdTask extends SpliceInTask {
         private final FileDescriptor fd;
         private final ChannelPromise promise;
         private final int offset;
 
         SpliceFdTask(FileDescriptor fd, int offset, int len, ChannelPromise promise) {
             super(len, promise);
             this.fd = fd;
             this.promise = promise;
             this.offset = offset;
         }
 
         @Override
         public boolean spliceIn(RecvByteBufAllocator.Handle handle) {
             assert eventLoop().inEventLoop();
             if (len == 0) {
                 promise.setSuccess();
                 return true;
             }
 
             try {
                 FileDescriptor[] pipe = pipe();
                 FileDescriptor pipeIn = pipe[0];
                 FileDescriptor pipeOut = pipe[1];
                 try {
                     int splicedIn = spliceIn(pipeOut, handle);
                     if (splicedIn > 0) {
                         // Integer.MAX_VALUE is a special value which will result in splice forever.
                         if (len != Integer.MAX_VALUE) {
                             len -= splicedIn;
                         }
                         do {
                             int splicedOut = Native.splice(pipeIn.intValue(), -1, fd.intValue(), offset, splicedIn);
                             splicedIn -= splicedOut;
                         } while (splicedIn > 0);
                         if (len == 0) {
                             promise.setSuccess();
                             return true;
                         }
                     }
                     return false;
                 } finally {
                     safeClosePipe(pipeIn);
                     safeClosePipe(pipeOut);
                 }
             } catch (Throwable cause) {
                 promise.setFailure(cause);
                 return true;
             }
         }
     }
 
     private final class EpollSocketWritableByteChannel extends SocketWritableByteChannel {
         EpollSocketWritableByteChannel() {
             super(socket);
         }
 
         @Override
         protected ByteBufAllocator alloc() {
             return AbstractEpollStreamChannel.this.alloc();
         }
     }
 }